1. Field of the Invention
The present invention relates to an air conditioner, and more particularly, to an apparatus and method for controlling a heating operation in a heat pump system, in which a continuous heating operation is provided.
2. Description of the Related Art
Generally, air conditioners are equipments to circulate a refrigerant through a reiteration of compression, condensation, expansion and evaporation. A combined cooling and heating air conditioner is recently developed. The combined cooling and heating air conditioner includes at least one outdoor unit and at least one indoor unit connected each other and uses a heat pump system that can selectively performs cooling and heating operations. In the air conditioner, at least one indoor unit is disposed at every installation space and a temperature of air is individually controlled at every installation space.
In the combined heating and cooling air conditioner, the cooling and heating functions are executed using a cooling cycle of flowing a refrigerant through a forward channel and a heating cycle of flowing a refrigerant through a reverse channel.
FIG. 1 is a schematic view illustrating a cooling cycle of a heat pump system according to the related art.
Referring to FIG. 1, the air conditioner includes a compressor 10, a four-way valve 11, an outdoor heat exchanger 12, an outdoor fan 13, an expansion valve 14, an indoor heat exchanger 15, and an indoor fan 16.
In the cooling operation, the compressor 10 compresses an inhaled refrigerant and discharges the refrigerant in a high-temperature and high-pressure vapor phase. The discharged refrigerant flows to the outdoor heat exchanger 12 through the four-way valve 11.
The outdoor heat exchanger 12 performs a condensation operation of exchanging heat between the refrigerant and an outdoor air using the outdoor fan 13, thereby condensing the refrigerant from the high-temperature and high-pressure vapor phase to a room-temperature and high-pressure liquid phase.
The expansion valve 14 makes the refrigerant from the outdoor heat exchanger 12 suitable for evaporation at the indoor heat exchanger 15. For this purpose, the expansion valve 14 expands the refrigerant, while creating a pressure drop.
The indoor heat exchanger 15 performs an evaporation operation of exchanging heat between an indoor air and the low-temperature and low-pressure refrigerant using the indoor fan 13. During the heat exchange, the refrigerant is expanded with reducing its pressure such that the refrigerant is evaporated into a low-temperature and low-pressure vapor phase while taking heat from the indoor air, thereby reducing a temperature of the indoor air.
The low-temperature and low-pressure refrigerant vapor from the indoor heat exchange 15 is inhaled into the compressor 10 again to complete one cycle of the cooling operation.
FIG. 2 is a schematic view illustrating a heating cycle of a heat pump system according to the related art. The heating cycle is opposite to the cooling cycle.
For the heating cycle, the four-way valve changes a flowing direction of the refrigerant in the channel (switching operation). That is, the four-way valve make a passage between the discharge side of the compressor 10 and an inlet side of the indoor heat exchanger 15.
A high-temperature and high-pressure refrigerant vapor is discharged from the compressor 10 and then the refrigerant flows to the indoor heat exchanger 15 via the four-way valve. The indoor heat exchanger 15 uses the indoor fan to facilitate a heat exchange between the high-temperature and high-pressure refrigerant vapor and an indoor air, such that the indoor air is heated and the refrigerant is condensed into a liquid phase.
The expansion valve 14 expands the refrigerant condensed at the indoor heat exchanger 15, while reducing the pressure of the refrigerant, in order to make the refrigerant suitable for evaporation. The outdoor heat exchanger 12 performs an evaporation operation of exchanging heat between an outdoor air and the refrigerant using the outdoor fan 13, thereby evaporating the refrigerant into a low-temperature and low-pressure vapor phase.
The refrigerant discharged from the outdoor heat exchanger 12 flows into the compressor 10 through the four-way valve to complete one cycle of the heating operation.
When the heat pump system performs the cooling operation, the outdoor heat exchanger 15 acts as a condenser and the indoor heat exchanger 12 acts as an evaporator. While the heat pump system performs the heating operation, the outdoor heat exchanger 15 acts as an evaporator and the indoor heat exchanger 12 acts as a condenser.
During the heating operation, frost is deposited on surfaces of tubes of the outdoor heat exchanger 12. The deposited frost disturbs the heat exchange of the outdoor heat exchanger 12, thereby reducing heat exchange efficiency and increasing heat loss and power consumption as well.
In more detail, the frost is deposited on the outdoor heat exchanger 12 when outdoor temperature is lower than a specific temperature, for example lower than 4° C. Since the frost disturbs the heat exchange, the heating operation cannot be continued. To remove the frost, the heating operation is suspended and a defrosting operation is performed through a reverse cycle (cooling cycle) for a predetermined time. Herein, there occurs a problem in the control of the indoor air, since the heating operation for heating the indoor air is suspended.
Further, referring to FIG. 3, the frosting operation is repeated with a predetermined time interval. Therefore, the frost deposited on the outdoor heat exchanger 12 is removed and efficiency drop of the outdoor heat exchanger 12 is prevented. During the defrosting operation, the indoor fan 16 is stopped and an outdoor louver is closed in order not to incur displeasure of user. Nevertheless, since the heating operation is discretely performed owing to the defrosting operation, the user feels displeasure.
Furthermore, since the heating operation and the defrosting operation are repeated periodically, the compressor 10 also repeats its driving and stopping operations frequently, so that compression loss of the compressor is generated